This invention relates generally to a downhole tool including a shock absorber and to the shock absorber itself. The invention relates more particularly, but not by way of limitation, to a downhole tool which carries an object into a well so that the shock absorber cushions it upon impact within the well. The present invention also more particularly, but without limitation, relates to such a downhole tool, also including an electronic temperature gauge, which can be dropped down a drill string to a drill bit connected at the bottom of the drill string.
From time to time in drilling, completing or producing an oil or gas well, implements need to be put into the well. These can be mechanically conveyed into the well such as on a wire line or a tubing string, or they can be dropped into the well. As used herein, something is "dropped" into the well when it is not connected to any other structure and is placed in the well to free fall or be pumped by fluid.
When an implement is conveyed or dropped into the well, sometimes it needs to be cushioned against shocks which might be transmitted to or through it upon the implement impacting the bottom of the hole or some other stop located within the well. To provide this cushioning, various types of shock absorbers have been proposed or used.
To give a specific example, reference will be made to a device for measuring temperature in a well. Measuring temperature in a well is important because, for example, a knowledge of the temperature at which cement will be pumped and a knowledge of the temperature at which the cement will cure are needed for designing and performing a desired job of cementing pipe into the well bore. These measurements are needed to improve the formulation of a particular cement composition to be used in a particular well, which formulation should allow adequate pumping time and desired set up time after pumping.
One type of device which has been put in a well to measure temperature comprises steel balls in which thermal paper is placed. The balls are dropped and circulated down the well bore and back to the top. During such a trip, the thermal paper records the maximum temperature. This device does not record other temperatures or indicate where the maximum temperature occurred.
Electronic temperature probes have also been used. These have been carried in on bundle carriers connected within a pipe string. This technique requires that taking of temperature measurements be planned with pipe string trips into and out of the well.
Temperature probes have also been run into wells on wire lines. Wire lines, however, are typically difficult to get into the well bore at the same time as mud is to be circulated, such as may need to occur during drilling. Additionally, running a wire line after circulation stops will likely not yield an accurate temperature value which would occur during actual circulation.
Static temperature buildup or different circulating temperature profiles cannot be measured except with the aforementioned bundle-carried temperature probe, but, again, that option has the expensive and time-consuming shortcomings of requiring the use of tubing string and coordinating with a trip of such string into and out of the well.
Therefore, there is the specific need for an apparatus which can obtain an accurate temperature at total depth without the use of a tubing string or wire line and there attendant shortcomings. Thus, such an apparatus is preferably of the type which includes a temperature probe that can take the desired readings and also of the type which can be dropped into the well. Because of the relatively delicate nature of the electronics in a suitable temperature probe, there is the further need for the apparatus to include a suitable shock absorber which will cushion the impact of the temperature probe upon impact at total depth. More generally, there is the need for an improved shock absorber for use in a well, which shock absorber can be part of an apparatus for carrying an object into a well.